Recently, recording density of hard disk apparatuses, which are a type of magnetic recording and reproducing apparatus, has been increasing by 60% per year, and this trend is expected to continue in the future. Therefore, a magnetic recording head and a magnetic recording medium which are suitable for realization of high recording density have been developed.
A magnetic recording medium used in a hard disk apparatus or the like basically includes a structure as described below. On a substrate containing an Al alloy coated with Ni—P through plating or on a glass substrate, a non-magnetic undercoat layer for determining crystal orientation of a Co alloy layer is formed from Cr or a Cr alloy such as CrW or CrMo through sputtering among other methods. A thin film of Co alloy, serving as a magnetic layer, is formed on the non-magnetic undercoat layer. In addition, a protective film predominantly containing carbon is formed on the magnetic layer, and a lubricant such as perfluoropolyether is applied onto the protective film to form a lubrication film.
In accordance with an increase in recording density of an apparatus such as a magnetic disk apparatus, there has been demand for a magnetic recording medium exhibiting excellent read-write conversion characteristics. Such medium exhibits magnetic anisotropy in a circumferential direction. Therefore, a magnetic recording medium including an aluminum alloy substrate coated with an NiP film through plating (hereinafter the substrate may be referred to as an “aluminum substrate”) is provided with magnetic anisotropy in a circumferential direction by forming grooves mechanically on the NiP film in a circumferential direction (hereinafter the procedure will be referred to as “mechanical texturing”).
Non-magnetic substrates, for example, glass substrates have been used in magnetic recording media, because glass substrates exhibit rigidity, excellent impact resistance, and evenness. Thus, glass substrates are applicable to an increase in recording density of magnetic disk apparatuses, in which the flying height of a magnetic head is reduced. However, mechanical texturing cannot be satisfactorily carried out on a glass substrate, and thus glass substrates have been used mainly in magnetic recording media exhibiting magnetic isotropy. Even when glass substrates are subjected to texturing, satisfactory magnetic anisotropy is not obtained, and thus glass substrates have been used mainly in magnetic recording media exhibiting magnetic isotropy.
In order to solve such problems, studies have been performed on techniques for imparting magnetic anisotropy to a magnetic recording medium including a glass substrate. For example, Japanese Patent Application Laid-Open (kokai) Nos. 4-29561 and 9-167337 disclose formation of a hard film on a non-metallic substrate, which can be subjected to texturing. Japanese Patent Application Laid-Open (kokai) No. 5-197941 discloses a hard film formed through sputtering, and subjected to texturing. Japanese Patent Application Laid-Open (kokai) Nos. 4-29561 and 9-167337 disclose formation of a hard film on a non-metallic substrate, which can be subjected to texturing. However, in each of the magnetic recording media disclosed in these publications, a hard film is formed through electroless plating. Consequently, the production process for the medium includes complicated steps, resulting in high production costs. Japanese Patent Application Laid-Open (kokai) No. 5-197941 discloses an NiP hard film formed through sputtering. However, after the NiP hard film is formed through sputtering, the film must be subjected to mechanical texturing. Consequently, the production process for the magnetic recording medium disclosed in this publication includes complicated steps, resulting in high production costs. Therefore, there has been a strong demand for a production process for a magnetic anisotropic medium in which, even when a non-metallic substrate is employed, the medium is produced through a simple production process at low cost, similar to the case in which an aluminum substrate is employed.